1. Field of the Invention
The invention relates to a method and apparatus for metal processing and, more particularly, to a method and apparatus for depositing and annealing metal films.
2. Background of the Related Art
Copper has gained increasing popularity as a metal interconnect in advanced integrated circuit fabrication. Copper can be deposited using electrochemical deposition from electrolytes such as copper sulfate or from electroless processes. Typically, electrolytes also contain carriers and additives to achieve certain desired characteristics in electroplated films. Some copper films, e.g., those deposited from electrolytes containing organic additives, exhibit “self-annealing” or re-crystallization behavior. For example, abnormal grain growth may occur in the as-deposited film such that film properties such as resistivity, stress and hardness may be adversely affected. The rate of grain growth may depend on the electroplating recipe, electrolyte types, as well as the organic additive concentrations.
These continual changes in microstructure at room temperature may lead to formation of stress-induced voids, or affect subsequent chemical mechanical polishing (CMP) behavior because of varying polishing rates for the film. Therefore, thermal annealing is usually performed on the as-deposited copper film to stabilize the film by promoting grain growth prior to subsequent processing.
Typically, copper films are annealed in a high temperature furnace or using rapid thermal anneal processing, both of which require relatively expensive and complex equipments. Furnace anneal of electroplated copper films, for example, is a batch process that is performed at an elevated temperature of typically about 400° C., either under a vacuum or in a nitrogen environment for at least about 30 minutes, which is a rather high thermal budget, time-consuming and costly process.
Therefore, there is a need for a method and apparatus for annealing copper that would allow film stabilization to be performed at a relatively low operating temperature in a simple gas environment with wide process windows, along with high throughput and relatively low cost.